1. Field of the Invention
The present invention generally relates to the microbial production of 2-keto-L-gulonic acid. More particularly, it concerns a process of preparation wherein 2-keto-L-gulonic acid is directly obtained from D-glucose by a mixed culturing of a plurality of microorganisms in a single fermenter or by a mixed contacting of a plurality of products obtained by treating said microorganisms in a single vessel.
2. Description of the Prior Art
The 2-keto-L-gulonic acid, which is useful as an intermediate for synthesizing L-ascorbic acid, has heretofore been commercially produced by the so-called "Reichstein's method", which is well known as a technologically established process. This method, however, comprises a number of complex steps and therefore any improvement in the overall yield is very difficult to achieve if not completely impossible. Therefore, there has hitherto been a number of proposals which contemplate a reduction in the number of steps and/or an improvement in the overall yield.
For instance, a biochemical method wherein 5-keto-D-gluconic acid, an oxidized product of D-glucose, is reduced to 2-keto-L-gulonic acid, a method of direct microbial conversion of L-sorbose into 2-keto-L-gulonic acid and the like are already known in the art.
These proposed methods have at least theoretically succeeded in the reduction in the number of the steps required for the production of 2-keto-L-gulonic acid but unexceptionally failed in the actual improvement in the overall yield and the feasibility or the steady operation of the total system.
Moreover, the attendant disadvantageous abundance of the resultant by-product both in terms of kind and quantity, difficulty in the separation of the intended product from the mixture which contains the by-products, and complexity in the operation, hinder the commercialization of these processes.